This invention relates generally to picture correcting apparatus for in-line type color picture tubes, and particularly to such apparatus using saturable reactors respectively connected in series with two horizontal deflecting coils.
Generally speaking, in color picture tubes used in color televisions, it is necessary not only to focus, at phosphor screen, the electron beams respectively emitted from three electron gun but also to converge the same. Therefore, in order to achieve satisfactory convergence of the three electron beams at the phosphor screen in conventional three-electron gun in-line type picture tubes, the horizontal deflecting magnetic field of the deflection yoke is made to have an intense pincushion shape, while the vertical deflecting magnetic field is made to have an intense barrel shape.
However, when the deflecting angle in a color picture tube becomes large such as 90 degrees or so, then pincushion distortion or barrel distortion occurs at the top and bottom of the raster when the deflecting magnetic field is arranged so as to obtain satisfactory convergence. As a result, such picture tubes are not practical. On the other hand, when the distortion at the top and bottom of the raster is satisfactorily adjusted, then positive-crossing misconvergence shown in FIG. 1 or negative-crossing misconvergence shown in FIG. 2 occurs and therefore the picture tube is not practical. In this way, in conventional color picture tubes, it has been difficult if not impossible to simultaneously satisfy convergence characteristic and top and bottom raster distortion.
The present applicant has already filed Japanese patent applications 56-91275 titled "PICTURE CORRECTING APPARATUS FOR IN-LINE COLOR PICTURE TUBE" and 56-111650 tiled "DEFLECTNG APPARATUS FOR COLOR PICTURE TUBE" as apparatus which resolve the above-mentioned problems, and corresponding patent applications in the U.S. Ser. No. 387,434 June 11, 1982, in the United Kingdom No. 8217,160 June 14, 1982, in West Germany No. P32 22 280.7 June 14, 1982, in France No. 8210,333 June 14, 1982, in Canada No. 405,016 June 11, 1982, in the Netherlands No. 8202,376 June 11.
According to this apparatus, as shown in FIGS. 5 and 6, reactors SR1a, SR2a or SR1b, SR2b, whose impedance varies at a vertical deflection period, are connected to respective horizontal deflecting coils L.sub.H1, L.sub.H2 among saddle shaped horizontal deflecting coils L.sub.H1, L.sub.H2 and a toroidal vertical deflecting coil which constitute a deflection yoke. The impedance of each of two circuits each including the horizontal deflecting coil LH1 or LH2 is varied such that impedance of one circuit increases or decreases when the impedance of the other circuit decreases or increases so as to vary the distribution of the horizontal deflecting magnetic field as a function of time, thereby obtaining satisfactory picture with convergence characteristics being corrected.
The reactors SR1a, SR2a in the apparatus of FIG. 5 have structure shown in FIG. 7. In this diagram, the references 1 and 2 are drum or spool type cores made of ferrite magnetic body, and the reference 3 is a permanent magnet which gives d.c. bias magnetic field to respective cores. On each of the spool type cores are wound coils RCH1, RCH2 connected to the horizontal deflecting coil and coils RCV1, RCV2 connected to the vertical deflecting coil. The coils are connected so that winding directions of the coils RCH1 and RCH2 are opposite to each other, while the winding directions of the coils RCV1 and RCV2 are the same.
The coils RCH1, RCH2, RCV1, RCV2 are connected to respective horizontal deflecting coils L.sub.H1, L.sub.H2 and to the vertical deflecting coil L.sub.V with a polarity shown in FIG. 5.
The deflecting apparatus of FIG. 6 has actual structure as seen FIGS. 8 and 9 where the deflecting apparatus is generally designated at the reference 19. The deflecting apparatus 19 is arranged such that reactors SR1b, SR2b, formed of a combination of coils wound around spool type cores, are attached to the vertical deflecting coil. Describing the apparatus further in detail, cores 4, 4' around which the vertical deflecting coil L.sub.V is wound are built in to be placed on a separator 6 made of a synthetic resin in which the horizontal deflecting coils L.sub.H1 and L.sub.H2 are built, and are arranged to face each other at a separating surface to be fixed by way of a clamp 7. A coil assembly 18.sub.1 formed of two coils 9.sub.11 and 9.sub.12 is built in a casing 15 provided on a terminal board 14. The terminal board 14 is secured to a cylindrical flange portion 8 of the separator 14 arranged to receive a rear bend-up portion of the horizontal deflecting coils L.sub.H1 and L.sub.H2, and the coil assembly 18.sub.1 is positioned on the surface of cores around the one facing portion 5 among two thereof of the cores 4, 4'. The coil assembly 18.sub.1 constitutes a saturable reactor SR1b because it is influenced by vertical deflecting magnetic field Hv' emitted outside the cores. Another coil assembly 18.sub.2, which forms a pair together with the coil assembly 18.sub.1, is positioned on the surface of cores close to the other facing portion 5', and constitutes a saturable reactor SR2b because it is influenced by vertical deflecting magnetic field Hv" emitted outside the cores.
As seen in FIGS. 8 and 9, the coils 9.sub.11, 9.sub.12 formed by winding a conductive wire around spool type cores 10.sub.11, 10.sub.12, and a permanent magnet 13.sub.1 which gives d.c. magnetic bias to respective cores in common, are all built in the casing 15 with a positional relationship as seen in these diagrams. The other coil assembly 18.sub.2 has the same structure as that of the coil assembly 18.sub.1, and comprises spool type cores 10.sub.21, 10.sub.22 with coils 11.sub.21, 11.sub.22 and a permanent magnet 13.sub.2 for giving d.c. magnetic bias which are all built in a casing 15.
As seen in FIG. 10, the above-mentioned coils 11.sub.11, 11.sub.12 are connected to each other so that they are in the same direction and opposite direction respectively with respect to the vertical deflecting magnetic field Hv', while coils 11.sub.21, 11.sub.22 are connected to each other so that they are in the same direction and opposite direction respectively with respect to the vertical deflecting magnetic field Hv", and as seen in FIG. 6, these coils are connected to corresponding horizontal deflecting coils L.sub.H1 and L.sub.H2. The permanent magnets 13.sub.1 and 13.sub.2 respectively have radial U-shaped grooves and are attached so as to be rotated when forcibly rotated, thereby the amount of magnetic bias being changed by rotation of the same.
However, even in the above-described apparatus, misconvergence occurs such that positive crossing occurs at the center of the picture and negative crossing occurs at the periphery as shown in FIG. 3, or in a small picture tube of 12-inch or smaller type of 90.degree. deflection, an inversed S-shaped misconvergence occurs as shown in FIG. 4 because the amount of misconvergence is large as shown in FIG. 1. It has been extremely difficult to correct misconvergence of this sort using conventional techniques, and the reason why will be described hereinbelow.
One approach of correcting the misconvergence pattern of FIG. 3 is the method described in the patent application 56-91275 "PICTURE CORRECTING APPARATUS OF IN-LINE TYPE COLOR PICTURE TUBE" previously field by the present applicant. The point of this method of correction is that the acting range of the control magnetic field acting on the coil bodies 9.sub.11 to 9.sub.22 is set to C in a graph of FIG. 11 showing the relationship between magnetic field and inductance, with the amount of the d.c. magnetic bias being made small from A to B. To obtain such an acting range C, it is necessary not only to reduce the amount of d.c. magnetic bias but also narrow the diameter of the spool type cores 10.sub.11 to 10.sub.22, and therefore, productivity lowers in the manufacturing process of the spool type cores or the spool type cores are apt to be broken during winding operation and these phenomena are problems on mass-production.
The S-shaped misconvergence shown in FIG. 4 is a phenomenon which occurs when the number of turns of the coils 11.sub.11 to 11.sub.22 is increased so as to increase the inductance variation of the saturable reactors SR1b, SR2b, and this is caused from the increase in ampere-turns of the horizontal deflecting current flowing through the coils 11.sub.11, 11.sub.22 and the number of turns of the coils 11.sub.11 to 11.sub.22. This point will be described in detail hereinlater.
At the present time, since the above-mentioned S-shaped misconvergence and the misconvergence shown in FIG. 3 cannot be completely removed, deflection yokes for color picture tubes are manufactured by finding a compromisable condition in which the error in convergence is scattered throughout the entire picture so that error appears as an average value at any points. Although it is ideal that an error in misconvergence is equal to or less than 0.2 mm in a super highly precise or highly precise picture tubes whose dot pitch is 0.21 to 0.33 mm, skilled workers are needed to achieve adjustment for reducing the error in misconvergence to such an extent, while it takes a long period of time and the result of adjustment are not necessarily satisfactory. Namely, there has been a drawback that it is impossible to mass produce low-cost deflection yokes having a misconvergence level that is required by the market.